His aunt, noting his heap of golden ringlets and his overall celestial glow, calls him "a beam of light with hair."

His sister, being four years old and Irish-bred and therefore incapable of saying "th", calls him "Ma-tyy-us."

His father and I call him “Mathias” because he's a junior, and it saves confusion to know him by this, his middle name.

Pretty soon, when it's no longer possible to mistake being insistently rambunctious, fascinated with matchbox cars, and full of sounds but not of words for being a toddler, most people will call him “autistic.”

These days, an awful lot of kids are called autistic -- about one in 106 American girls, one in 70 American boys. And there is an awful lot of raging about why this is.But, curiously enough, in the wake of our precious son’s being diagnosed with this widely dreaded disorder, I am not raging at all.

Since this whole issue arose, I have felt many moments of the most abject gratitude.

Outwardly, I am scrambling, searching out therapists, debating strategies, and devouring all manner of research. But inwardly, I am sitting very still, letting a silent but seismic shift proceed at my core.

If you have healthy children, who have passed all their tests and met all their milestones, you might wonder, as I used to, what it would be like if one of them didn’t; what would happen if you brought some concern to the doctor and he didn’t brush it away like a crumb, but examined it like a rare and troubling specimen, then looked up at you and nodded as your heart stopped cold: yes, you were right to fear what you did.

This is what happens, or at least what is happening to me.

Right away, the world becomes small, dark, and clear. Right before the diagnosis, at the end of February 2010, I was fired up on various mental fronts. I was eager to get up to speed on China; catch up on Iraq; determine whether my recent joining of the Barack Obama fan club was based on anything more solid than the fact that everybody else seemed to be burning their membership cards. Right after, I just wanted my boy to look at something he liked and point.

As of New Year's, I had never heard of Temple Grandin, an autistic woman who has multiple Ph.D.'s, a big-time career designing humane slaughterhouses, and Clare Danes playing her in an acclaimed HBO biopic. By March, having defied the scary (but also questionable) statistics on adults with autism -- half cannot speak; only 15 percent have real jobs -- she was the prize I kept my eye on. On Valentine's Day, I did not know "casein" from a refried bean. By Easter, I could tell you that it is a milk protein that, one theory has it, many autistic people have trouble digesting, to the detriment of their brain function, and my default mental activity had become weighing the wisdom of stripping it ruthlessly out of my little dairy lover's diet.

The world darkens. Until this happened, I will admit, my personal life was so happy that I could practically feel the urge to blink in the sun of my good fortune. Now, the sun has certainly not gone out. But a certain shadow has been cast, even in the furthest reaches of the mind. All of a sudden, the idlest dreams look different: should we leave Ireland someday, and if so, why, and bound for where? This used to be a matter of what destination fascinated, remunerated, beckoned: China, the Continent, home to America? Now, even in the cloudiest of musings, it all depends on what he needs and where it can be had.

Far stranger than the future’s falling into doubt is the fact that the past does, too. After all, no one can really know what is going to happen, but everyone should have some idea of what already has. I don’t. Although I now stand apprised that autism has come to live with us, I don’t know when it got here, or how. Thus, the familiar, gently bending world has just become an unrunnable obstacle course of unseen, retroactive hazards. Rationally or not, all sorts of things -- vaccinations, antibiotics, certain types of house paint, vinyl flooring, sunscreen, and the fact of his having been born a boy -- have gone from being a list of random incidentals to a worrisome trail of could-be-causative clues.

Then again, maybe the world hasn't darkened so much as split into two screens on opposite ends of the light spectrum. Since this whole issue arose, I have felt many moments of the most abject gratitude I have ever known -- most of them instantly followed by moments of the most howling anguish: gratitude that, by luck of the draw, our family can map out Mathias' path from here solely with an eye to giving him the best shot at the best life, which therefore may end up being a fantastic shot indeed. The anguish is that so many parents can't do any such thing; that so many parents have to spend months and years waiting to get their children diagnosed, watching them deteriorate all the while, and then more months and years chasing down what skinflint help they can. I always admired Ted Kennedy’s commitment to health-care reform and saw no reason to doubt his claim that that commitment had been awakened by his son’s struggle with cancer, when he got to know other families with the same terrible battle and no money to fight it. But I never could quite believe that anyone could be actively sickened by what was happening to other people’s children at the very time of being so actively consumed by what was happening to one’s own. I believe it now.

The world becomes clear, in no uncertain terms. You see everything that you have for exactly what it is. If what you have is a shallow set of friends, a cold bunch of blood relatives, and a weak marriage, the clarifying of this must be horrible, as final and fatal as the realization that you are gunning the car in the wrong direction down a one-way street and there’s an eighteen-wheeler barreling at you. Or so I imagine, because I have the exact opposite on all three counts -- and I feel more certain of this than I possibly could have when life was a filet of lemon sole, light and smooth, with all the bones taken out for me.

If the reality of all relationships becomes clear, that of the marital relationship starts flashing neon. Ladies, far be it from me to discourage you from marrying the kind of guy who will get you a world-class diamond. But trust me, what you really want is the kind of guy who will be with you -- really with you -- as it dawns that what you want is what you dread: a world-class diagnosis.

This is especially true when the condition in question is one that can be so easy, and so tempting, to deny. If you are anything like me, and you ever entertain worries about your generally lovely child like those I had about mine, go ahead and write off whatever time you have to wait between booking a diagnostic appointment and actually going to it. Trust me, you will spend half the interim scaring the hell out yourself, and the other half telling yourself not to be ridiculous. One minute, you will think there could be something amiss, the next minute you will think there couldn’t be. With the efficiency of the delete button on a keyboard, the first, frightening thought is cut and the second, comforting one is pasted. For the former, there’s the friend's child who is four months younger than yours and speaking in real phrases. For the latter, there’s that other friend’s uncle who didn't talk till he was six but grew up to be a rich inventor, or the sibling who hardly said a word and then one day woke up and spouted forth in full sentences in two languages (as our daughter did.) Or everybody’s favorite, Einstein, whose parents thought he was mentally backward till he was nine (or was it six? Or fourteen?)

With autism, even if both parents are smart and wonderful and well-meaning, one can so easily fall into denial and pull the other one down into it, too.

Unhappy as I was to receive the diagnosis, I was happy -- ecstatic, even -- that this had not happened with us; that my husband and I had both become concerned to about the same degree at about the same time, and that once the possibility of autism crept onto our horizon, neither one of us had had the urge to run away from it. On the contrary, we both had the powerful urge to run toward it; to figure out whether it was really there, and if so, to get a good hard look at it. As a result, Mathias was diagnosed at a young enough age that serious improvement is a serious possibility.

If our son’s autism is a burden, this is a huge blessing within it, and one morning, I woke up flooded with gratitude for it. Turning to my husband, I said, "I'm so glad you're not one of those jerks who'd say, "there's nothing wrong with my son."

Without the blink of an eye or a drop of irony, too quickly to have made it up, he shot right back: "There is nothing wrong with my son."

As it happens, this is absolutely true.

A little too true for me, at first. Having always had the most pathetic crush on my son, I did not instantly see his problems as problems. Around Christmas, when he started hopping out of his bed in the mornings, trotting up to mine, and blowing "woo--ee-oo" into my sleeping face, I wasn't worried. I was delighted; it was like having my own personal rooster. When he greeted the sight of ice cream, as he invariably has, with a euphoric face, trembling lips of joy and a hearty round of applause, I was so besotted, I didn't even think to wish he asked for it verbally instead. When, eyes closed and face turned skyward, he drank in the average sun and air with the rapture of a prisoner set free, I wasn't concerned. I was envious.

When he was first diagnosed, I beat myself up for failing to recognize such red flags right away. But then, I gave myself a break -- and not just because it wasn’t all that long before even my window of delusion slammed shut. More than that, it was because I think that that mother-lovey lag-time had taught me a very important lesson: that just because my child has a disorder does not mean that he doesn’t have anything else.

Reader, he has so much else.

I could make a great big list, but everything on it could be distilled into one factor. First, last and always, he has light. If you saw him, you would see it: light in his eyes, light in his face, light in the bright, strange sounds he loves to make.

I don’t know where Mathias’ IQ will end up, but I can swear that he is literally brilliant. He beams from every pore.

And it is in that light that I can see what I have come to see most clearly of all: the simple beauty of this complicated child.

In the fullness of time, Mathias might turn out to be a blazing superstar. He could turn out to be a dependent for life. I don’t know. But this I know with more conviction now than I knew it before anyone called him autistic: There is nothing wrong with my son.